Niko's Amplifier build.

[N4LTA]

Niko sent me a couple of SRS551 transmitter tubes to build a 200 Watt linear to use with the 4SQRP Nouveau transceiver. It uses two of these unique looking tetrodes.

I just about have the power supply complete. I have the power transformer and chokes mounted and have completed the power supply PC Board.

The board has the snap in filter caps  (three 220uF at 600 volts in series) and the screen regulator components installed and tested. The initial try will be with approximately 420 volts on the screens and 1200 volts on the plate. The power transformer is a 1200 volt Hammond with a 10H choke in the negative lead. The  screen supply  uses the same transformer wired like the old "economy" circuit and a single 220uF cap and a smaller 100mA choke. It uses four 100 volt 5 watt Zeners as a reference voltage for the T047 MOSFET.

I have a separate bias supply done that I can vary  from -30 to 0 volts. I am expecting the proper bias to be near -16 volts.

The screen supply is one that has been used quite a few times on this board and very similar to the regulated supply for my PWM Modulator power supply. It is  current limited at about 65 mA.
A high voltage 2N6520 pnp transistor works in the current limit circuit. This circuit has been publish on this site also.

Thanks all for providing the basis circuits for the power supply and now I'll start the RF section. It will be based on the following circuit

This is a photo of the completed power and screen supply board

[K8DI]

Would you be able to share a better image of the schematic? I can't zoom in enough to read it.  Also, is that PSU board available? it's pretty much what I've built from circuits found here on terminal strips; a board would be handy.

Ed

[w9jsw]

I would also like to see the schematic larger, Pat.

Ed - this circuit is very similar to another I have made on a board. I am going to make a few changes and then have some more board made. Will let you know when I have some.

The circuit is page 2 of the pdf.

They will look like these. I add a single cap and a bridge to feed the circuit. Going to try to make it a bit smaller this time.

John

[N4LTA]

The schematic is from the Valve Museum page. I am not allowed to share the larger version. I had to join the group to get it. You can find it on the Valve Museum page  by searching SR551 tube.

The PCB is in Express PCB format. I'll share it if you like but the program does not generate Gerbers. I plot the layers and make my own boards generally 1 sided.

[w9jsw]

Pat,

Did you make any circuit changes beyond what I sent to you?

Here is a board from the same schematic. I was not able to make it any smaller. It mounts nice on a 100mmx100mm heat sink. I get them for around $6 each on the 'bay.

Will get some made up. I need one for my project anyway. Rest I can make available to others interested in the design or even post it as a shared project on Oshpark. That is more expensive, however.

John

Update - ordered the boards. Should be here in a week.

[N4LTA]

I got a little more done this afternoon. Got all of the iron mounted and the two boards mounted and punched the SRS551 tube socket holes. Got them mounted. May get the rest of the 120 volt wiring and get the filament wiring done later today. My grand daughter (age 2) is here until Christmas Eve and she slows things down a bit,but it is a fun slowdown.

I'll have to wait for Tuesday until the 2 watt ceramic composition resistors show up for the parasitic suppressors before I can wire the tubes

Right now I am planning to use a short pi wound plate choke from an old transmitter  and will use a high voltage feed through insulator as a feed point for the parasitic suppressors - feeding the RF to the top side. I'll mount an NOS Centralab 10KV 1000pF door knob to the top of the feed thru and pick off the RF to the tank at that point. I have a 250 pF ceramic variable to tune the plate and will use a triple gang 356 pF rx type variable to tune the load. Initially it will  be for 75 meters but if it works well I'll ad 40 meters for sure and maybe 20 meters  and 160.

I may have a front panel laser cut if this thing works well. I had some chassis tops cut in stainless and they worked very well. Price was very reasonable.

If anything looks stupid, please let me know.

Thanks in advance

Pat
N4LTA

[N4LTA]

Got some time to work on this project. The  original power tested ok but no load voltages were too high to suit me. Big electrolytics blowing up is never fun! I built a new board with three 550 volt electrolytics for the plate supply (1200 volts) and two 450 volt caps for the screen supply (600 volts). The two 10H chokes are doing their job, keeping the no load 1200 volt supply a bit over 1200 volts and the 600 volt supply at 606 volts.

I mounted a plate choke underneath and bypassed it with a .001uF 6 KV cap. I'll add the parasitic suppressors next and the screen wiring. My plan is to use a HV feed through insulator to  couple the RF to the top side and mount the pi net on the top. It will be close fit. I have a 300pF 2 KV variable and a three gang 365 pF rx type variable to tune the load

Burning in the power supply for 8-10 hours and running the filaments during that time.

I don't have a lot of data on the tube. I assume the tube filaments are not quick heating, so I need to add a filament on switch separate  from the HV.

Trying to keep the cathode and control grid as far from the plate  circuit as possible. I suspect that I will have to add a divider underneath anyway.

Pat
N4LTA